In a CVT, a belt which is made up from stacked rings, in which plural metal rings are stacked, serves as a power transmission. In general, the metal rings are fabricated by implementing a predetermined heat treatment such as a solution heat treatment, an aging treatment, a nitriding treatment or the like, with respect to pre-form bodies, which are formed by cutting a cylindrical drum made from maraging steel into predetermined widths.
In order to carry out such a heat treatment, generally, a plurality of such metal rings is retained on a conveyance rack and the multiple rings are conveyed simultaneously into a heat treatment furnace. In this condition, heat treatment is carried out together with the conveyance rack. As a conveyance rack of this type, for example, there is known the conveyance rack disclosed in Japanese Laid-Open Patent Publication No. 2007-191788.
The conveyance rack disclosed in Japanese Laid-Open Patent Publication No. 2007-191788 includes a plurality of retaining shafts, which are erected on a base, wherein a plurality of ring seats, formed in the shape of abacus beads, are attached to each of the retaining shafts. In such a structure, each of the metal rings is interposed between each of adjacent ring seats, as shown in FIG. 4 of Japanese Laid-Open Patent Publication No. 2007-191788.
On the other hand, as disclosed in Japanese Laid-Open Patent Publication No. 10-251741, a plurality of piece members are disposed respectively on a plurality of retaining shafts, and intermediate base boards to be processed into aluminum base boards for magnetic disks are gripped between each of the adjacent piece members.
In this manner, retention of workpieces having annular or disk shapes as a result of being gripped between respective piece members, which are provided on a plurality of retaining shafts, is performed in various technical fields.